these are brads... they're also called as paper fasteners.
A brad is a type of embellishment, used as a decoration for card making or scrap booking. They are usually inexpensive embellishments and require no special tools.
A brad has 2 prongs (the legs or the parts that stick out). How to use a brad? First, punch a small hole or use a sharp cutter to slit through your card or paper, just a little, so that the prongs can go through it. Then, push the prongs through the slit/hole and split the prongs apart. That way, the brad is attached securely to the paper.
There are many types of brads in various colours, shapes, sizes and materials. As long as it has 2 prongs, it's called a brad. I love using brads in my card-making because it is easy to use and it give dimension to the card. You can use brads to layer your cards or to attach flowers to it, like i did in my minnie mouse pic frame.